The leader of the Islamist insurgency in the Northern Caucasus, Doku Umarov, may have been among the 17 militants killed in a special operation by the Russian security forces, reports said on Tuesday.
However the reports were not confirmed and Russian officials have repeatedly over the last years prematurely announced the death of Umarov, only to be proven wrong later.
Umarov, whose Caucasus Emirate rebel group aims to enforce Islamic rule across the Northern Caucasus, claimed organising both the Moscow metro bombing one year ago and the suicide attack at Domodedovo airport in January.
The Interfax news agency quoted security officials as saying that "according to preliminary information" Umarov was killed in Monday's special operation in Ingushetia, along with another militant leader Aslan Byutukayev.
However officials added that a full-scale identification has not been carried out.
"Among the 17 killed were bodyguards of Umarov. This allows us to believe that Umarov himself was killed," a security source in Ingushetia told the news agency.
The operation Monday evening involved a highly unusual precision aerial strike on the base of the militants, and killed, among others, Supyan Abdylaev, a militant who always accompanies Umarov, the source said.
"There were several militant leaders at the base," said Ingushetia's pro-Kremlin leader Yunus-Bek Yevkurov, acknowledging it was not yet confirmed if the Caucasus Emirate leader is among them.
He added that two brothers suspected of involvement in the suicide blast in Moscow's Domodedovo airport that killed 37 people and wounded more than 100 in January this year were also captured on Monday.
The Yanayev brothers were detained after relatives of the suicide bomber Magomed Yevloyev told security services of their connection to the militants.
Russia on Tuesday was also marking one year since the March 29, 2010 metro bombings, when 40 people were killed and dozens wounded by two female suicide bombers during the morning rush hour.
The investigative committee said Tuesday that it had identified all of the direct organizers of the attack, including 22-year old Dagestani Gusen Magomedov, who accompanied the suicide bombers to Moscow, but is now at large.